Why do we sleep?

Aristotle believed that during sleep the body emitted certain vapors, which helped disperse food from the stomach to the rest of the body. In a similar vein, some researchers in the early 20th century maintained that chemicals such as carbon dioxide, cholesterol and lactic acid collect in the brain during waking hours, and sleep provides an opportunity for these chemicals to be redistributed throughout the body.

Another popular theory postulated that sleep was merely a means of regaining energy. It seemed unlikely, however, that this explanation was complete, as it failed to account for the evident need for REM sleep in particular. Newborn babies, for example, spend about half of their sleeping time in the REM state; evidence of an REM state has also been observed in most mammals, birds, and reptiles. Further, experiments have shown that people deprived of REM sleep become excessively sensitive, lose the ability to concentrate, and suffer poor recall. In contrast, those deprived of non-REM sleep experience fewer and shorter-term difficulties. It thus appears that in non-REM sleep, the body and mind are resting and regenerating. REM sleep, on the other hand, seems to be less physiologically but more psychologically important.

The nature of dreams

Despite the large body of research into sleeping patterns, the human need to dream continues to evoke more questions than answers. Are dreams a way to dispel unwanted waking experiences? Are they a means of processing daily events? Or are they an exercise for a part of the brain that remains dormant during the waking hours?

As a result of studying dreams in laboratories, which allows for "on the spot" dream retrieval, scientists have discovered that the vast majority of dreams, including those experienced during an REM state, are mundane, highly realistic experiences, as opposed to bizarre, random occurrences. Further, dreams are also not usually faithful reproductions of memories; rather, they are novel experiences which have a thematic coherence, much like a story or novel. In most dreams, the dreamer experiences emotions that are appropriate to the particular situation in the dream.

It seems likely that dreaming has a number of complex and interrelated physiological and psychological functions. One thing is clear, however: the dreams of each individual encapsulate aspects of his or her particular psyche and circumstances, including his or her life situation, relationships, and experiences. An awareness of our dreams, therefore, may help us to increase our understanding of our thoughts and emotions.